The invention relates to scintillation cameras, and more particularly relates to compensating for the effect of finite angular resolution of collimated scintillation cameras.
In a conventional scintillation camera as used for example in medicine, a collimator is mounted to the face of the camera. The collimator collimates the radiation which has passed through the patient before that radiation strikes the sensitive crystal surface of the camera.
Each channel of an ideal collimator would be infinitely narrow. If this were possible, each channel of the collimator would permit only on-axis rays to reach the sensitive surface; all other rays, no matter how slightly off-axis, would be blocked. Put another way, the scintillation camera system would have an infinitesimal angular resolution because no off-axis ray would ever be able to get through the collimator.
An ideal collimator cannot be manufactured. Each collimator channel must be finitely wide and deep. Hence, off-axis rays can and do reach the sensitive crystal surface, so that the angular resolution of the camera is finite.
Because of this, there is an inherent limitation on the resolving ability of the camera. As a result, highly detailed regions of the image cannot be accurately depicted because the detail is finer than the camera's limit of angular resolution.
The finite angular resolution of the system becomes increasingly important with increasing distance between the patient and the sensitive crystal surface. This is because the region subtended by the minimum resolvable angle becomes larger with increasing distance from the collimator. Therefore, the detail in the final image of the patient depends upon the distance between the imaged region and the camera head. To maximize this detail, a technician must spend the time to minimize the distance between the camera head and the patient over the whole range of motion of the camera head. This decreases patient throughput through the scintillation camera.
It is known to apply correction techniques to compensate scintillation camera systems for various factors, but the factors do not include compensation for finite angular resolution. For example, there exist conventional techniques by which the camera is corrected for spatial nonlinearity and nonuniform energy response; in these correction schemes, a fixed camera is exposed to e.g. a test pattern and/or a full-field flood in order to derive correction factors to be applied to incoming image data on an event-by-event basis. These latter techniques correct neither for finite angular resolution nor for any collimator-related factor.
One object of the invention is to provide a scintillation camera system which corrects for the finite angular resolution of its collimator.
Another object is to provide such a system in which distance between the patient and the camera is less critical a factor than it is now.
Yet another object is to provide such a system which permits the in situ compensation of individual collimators.
Still another object is to provide such a system which has a better angular resolution than its constituent collimator.
Still a further object is to provide such a system in which it is possible to improve the angular resolution without changing the collimator.
Yet a further object is, in general, to improve on known devices of this type.